A fluid conduit assembly is provided that includes a first conduit coupler, a second conduit coupler and a lock. The second conduit coupler is mated with the first conduit coupler at a threaded interface. The lock is configured to rotationally fix the first conduit coupler with the second conduit coupler. The lock includes a flange, a clip and a fastener. The flange is arranged with the first conduit coupler. The flange is configured with a plurality of flange apertures arranged circumferentially about an axis of the first conduit coupler. The clip is arranged with the second conduit coupler. The clip is configured with a clip aperture. The fastener is mated with the clip aperture and any one of the plurality of flange apertures.